나노기공을 함유한 유기 실리케이트 박막의 유전 및 광학 특성에 관한 연구

학위논문(박사) --서울대학교 대학원 :응용화학부,2007.Docto

Cake Reduction Mechanism in Coagulation-Crossflow Microfiltration Process

Cake layer in crossflow microfiltration (CFMF) can be reduced by coagulation, enhancing membrane flux. This is because enlarging particle size by coagulation Increases shear-Induced diffusivity and the back-transport of rejected particles. However it is known that the enlarged particles are disaggregated by the shear force of the pump while passing through it. This study is to look at the disaggregation in relation with cake layer reduction. Kaolin and potysulfon hollow fiber microfilter are used for experiment. The reduction of cake resistance by coagulation is observed in a range of 17% to 53% at the various coagulation conditions. The particle size analysis results of the experiments show that aggregated particles In feed are completely disaggregated by pump but re-aggregation of particles occurs In membrane. This suggests that the re-aggregation of particles is critical to cake reduction and flux enhancement, since the aggregated particles are completely broken. The mechanisms for re-aggregation In membrane are the same with those for coagulation in feed tank. Charge neutralization is better for CCFMF than sweep flocculation although it has two drawbacks in operation

Modeling of Critical Flux Conditions in Crossflow Microfiltration

In the process of crossflow microfiltration, a deposit of cake layer tends to form on the membrane, which usually controls the performance of filtration. It is found, however, that there exist a condition under which no deposit of cake layer is made. This condition is called the sub-critical flux condition, and the critical flux here means a flux below which a decline of flux with time due to the deposit of cake layer does not occur. In order to study the characteristics of the critical flux, a numerical model is developed to predict the critical flux condition, and is verified with experimental results. For development of the model, the concept of effective particle diameter is introduced to find a representative size of various particles in relation to diffusive properties of particles. The model is found to be in good match with the experimental results. The findings from the use of the model include that the critical flux condition is determined by the effective particle diameter and the ratio of initial permeate flux to crossflow velocity